1. Field of the Invention
The field of the present invention relates to electromagnetic emergency exit door lock systems. More particularly, the present invention relates to tamper-resistant time delay emergency exit electromagnetic door lock systems.
2. Description of the Related Art
Electromagnetic locks are commonly used in xe2x80x9cdelayed exitxe2x80x9d systems. The purpose of a delayed exit system is to allow people to exit a building immediately in the event of an emergency, or after a 15 to 30 second delay in a non emergency situation while at the same time providing an acceptable measure of security against unauthorized entry or exit. Typically, a person who wishes to exit in an emergency activates the door by pressing down on a spring biased push bar sometimes called a xe2x80x9cpanic barxe2x80x9d mounted on the door. Alternately a lever or door knob may be turned. This initiates an audible alarm. If the person maintains the initiate signal by holding the panic bar down for the duration of a xe2x80x9cnuisance delayxe2x80x9d period which is typically 1 to 3 seconds, the system will then begin a delay known as an irrevocable release or egress delay. At the end of the egress time delay the door will open. The egress time is typically 15 or 30 seconds under most building codes.
The purpose of the nuisance delay is to cope with accidental striking of the door or push bar. When someone inadvertently presses against the push bar, an audible alarm warns the person away from the door. If the initiate signal is maintained for less than the duration of the nuisance delay period, the door will xe2x80x9cresetxe2x80x9d when the initiate signal stops and will therefore not release at the end of the 15 or 30 seconds. This maintains security and also saves building staff from the necessity of going to the door and re-locking it if it had released. The nuisance delay concept was intended to not only deal with accidental striking of the door, but with casual vandalism as might be expected from young persons who would push the door, hear the alarm, and then run away. On the other hand, if the initiate signal is maintained for longer than the nuisance delay period, release after 15 or 30 seconds becomes irrevocable. Such systems are in broad use, particularly in retail establishments where they greatly reduce theft loss while complying with building codes that require a minimum number of emergency exits.
One of the earliest electromechanical delayed exit systems is disclosed in U.S. Pat. No. 4,257,631 issued to Logan. Logan discloses a switch located within a push bar mounted on the door to sense when somebody attempts to exit the building. There are two significant drawbacks to this design. First, on existing doors a push bar is already present so it must be replaced at relatively high cost with a push bar equipped with a switch. Second, the wires to the switch within the push bar must be routed from the door to the frame which carries the electromagnetic lock. This requires either an electric hinge which is costly to purchase and install, or a xe2x80x9cdoor cordxe2x80x9d which is looped between the door and frame. Such door cords invite vandalism as the wiring is exposed.
U.S. Pat. No. 4,609,910 issued to Geringer discloses a delayed exit system in which two bolts which mount the armature plate to the door are allowed slack in their holes. When the door is pushed, the door can move slightly, thereby taking up this slack. The door remains securely held by the electromagnetic lock but the slight motion can be detected by a plunger type switch. The switch initiates the delay without the need to supply a switch equipped push bar or to route wires into the door.
One problem with this system is that it is prone to false initiation. To avoid having to precisely align the door and the door frame, the push bar-activated latch is often allowed a significant amount of slack within its securing recess. Wind or vandals rattling the door can take up the slack provided in the bolts of Geringer, thereby activating the switch and initiating the delay even though a person had not intended to exit. This constitutes a type of xe2x80x9cfalse alarmxe2x80x9d.
A further drawback of this design is that it is vulnerable to tampering. The plunger switch can be taped down such that the switch is incapable of recognizing when the door has been pushed away from its fully closed position in an effort to exit the building. This type of tampering may be performed by building guards for example who desire to increase security at the expense of egress safety, or who do not wish to have to check on the door when it is activated, either by someone who has exited or by a false initiation. This creates a hazardous and potentially fatal situation.
A similar design is disclosed in U.S. Pat. No. 4,652,028 issued to Logan et al. As in the Geringer design, slack is created by the use of bolts whose heads fit loosely within the armature plate. This design is prone to similar false initiations. Since the Logan et al. design uses a Hall effect sensor to detect the slight movement of the door provided by the slack in the bolts, the mechanism cannot be overridden by the use of tape. However, the system may still be tampered with by the application of an external magnet, which can disrupt the operation of the Hall effect sensor.
A further design is illustrated in U.S. Pat. No. 4,915,431 issued to Bailey. As in Geringer, Bailey employs a mechanical plunger switch, but the switch is positioned in the center of the armature which makes it relatively immune to tampering. As in Geringer, the slack that allows door movement is created by allowing mounting bolt heads to move slightly within the armature. This design is also vulnerable to false initiation by rattling of the door caused by wind or vandals.
A still further design is illustrated in U.S. Pat. No. 5,065,136 issued to Frolov et al. In this design, the electromagnet body is permitted to pivot slightly in response to pressure on the door. The rotational action of the top of the electromagnet creates a small gap between the electromagnet top and the door header which permits a spring biased switch to change state by its trigger moving into the gap. This design is also prone to tampering. Someone working within the facility can temporarily pivot the electromagnet body down and insert a piece of tape to prevent the switch from moving into the gap. This would prevent the switch from being triggered by movement of the door.
An armature mount assembly is disclosed in U.S. Pat. No. 5,184,856, issued Feb. 9, 1993 to Waltz. The disclosure teaches a mount that allows the armature to be pulled outward from the door a small distance to contact an electromagnet mounted to the door frame. However, there is no teaching of an armature mount that allows the door to be opened outwardly a considerable distance while the armature is held against the electromagnet.
Accordingly, it is a general object of this invention to provide a delayed exit door control system that can be economically implemented for retrofit applications.
It is a further object of the invention to provide a delayed exit door control system that is resistant to false initiations by rattling caused by wind or vandals.
It is a further object of the invention to provide a delayed exit door control system that is resistant to tampering, either from casual vandals or by personnel within the facility.
It is also an object of the invention to overcome disadvantages of the prior art.
To achieve these and other objects, the present invention includes an electromagnet mounted to a door frame, an electromagnet armature mounted to a door facing the electromagnet, and an armature mount allowing considerable outward movement of the door with respect to the frame while the armature is held against the electromagnet. One way of doing this is by providing an armature mounting bolt (sometimes referred to as a xe2x80x9csex boltxe2x80x9d within the industry) that includes a novel internal spring biased plunger to which the armature is mounted. The spring biased plunger extends out the back of the armature mounting bolt, and is threaded so that the armature may be mounted directly to the back of the plunger. The spring allows the armature to be pulled away from the armature mounting bolt as for example by someone pushing on the door to initiate a delayed exit sequence, and return towards the bolt once the external force is removed.
The spring provides a bias force to assist in the return of the door to its fully closed position in the event that someone intentionally or unintentionally pushes the panic bar on the door, causing the door to open to its activation position momentarily and hence initiating the nuisance delay. Provided that the vandal or other person releases the door before the end of the nuisance delay period, the door will be assisted in returning to its fully closed position, and the door will remain locked. This provides a significant advantage over prior art systems that lack a mechanism for positively returning the door to its fully closed position, as for example systems that employ slack in mounting bolts.
The spring biased plunger of the present invention moves within the space of the armature mounting bolt, which is mounted through a hole in the door. The plunger therefore can move through the volume defined by the door, as much as the entire thickness of the door and even more if the armature bolt hollow interior is allowed to be longer than the thickness of the door. This provides a much greater travel distance than was possible with prior art systems that relied on slack movement of mounting bolts within the volume of the armatures themselves. Since conventional armatures are typically steel plates on the order of one-half inch (1.27 cm) thick, the prior art systems were limited to significantly less than that amount of movement (on the order of xe2x85x9xe2x80x3 or 3 mm). With the present invention, the door movement distance required for activation can be set at a sufficient distance that mere rattling of the door within the panic bar latch cannot initiate the system. Rather, the panic bar latch must be released and the door pushed by an individual a sufficient distance to activate the system. For example, on a 1 xc2xexe2x80x3 (44.45 mm) door, the most common commercial door thickness, the present invention permits door movement of up to 1.1xe2x80x3 (28 mm). This amount of movement is well beyond the distance a door could be moved by rattling but is less than the thickness of the door which precludes the insertion of a crowbar so it represents an ideal choice.
Note that although the preferred embodiment of the present invention employs a spring within the armature mounting bolt to bias the moving plunger within the armature bolt towards assisting reclosure of the door, the utility of this aspect of the invention is not dependent on the presence of the spring but rather on the ability of the plunger to move a substantial distance within the armature bolt. In an alternate embodiment, the spring could be deleted because commercial doors of the type that receive delayed exit locking systems almost invariably include a door closer which externally replicates the functions of the spring.
The present invention also includes a novel sensor system for detecting movement of the door to its activation position. The sensor system includes a permanent magnet mounted to the door, and a triad of magnetically activated reed switches mounted to the door frame. When the door is in its fully closed position, the permanent magnet activates (xe2x80x9cenergizesxe2x80x9d) the first two reed switches, which are redundantly connected in case either switch fails. Movement of the door to the delay initiating position de-activates the two reed switches. This signals a system controller that someone is attempting to exit. The first two reed switches by themselves could be tampered with by placing a large permanent magnet into proximity with these switches, which would fool the reed switches into sensing a magnetic field even though the door had been moved to its activation position. To prevent this, a third tamper detection reed switch is added to the system. This tamper detection reed switch is not activated (not xe2x80x9cenergizedxe2x80x9d) by the permanent magnet mounted to the door, but will be activated by the presence of a second permanent magnet introduced for tampering purposes. Thus, the system automatically detects when someone brings a second permanent magnet into proximity with the sensor in an attempt to tamper with it. In the present invention, such tampering immediately initiates delayed exit which preserves the safety function of the door as well as sounding an alarm.
It should be understood that the part of the present invention which prevents tampering can be separated from the previously described part which permits extensive door movement prior to initiating the exit delay sequence. In certain applications, tampering is not an important concern and the removal of the anti-tampering parts from the invention results in a much lower cost and less physically obtrusive system to be mounted on the door.
In one aspect, the present invention includes a door equipped with an armature for locking engagement with an electromagnet mounted to a door frame; an armature mounting bolt mounted within a hole in the door; a spring mounted within the armature mounting bolt for providing a bias that draws the armature to the door and urges the door to its fully closed position; a detent within the armature mounting bolt for allowing a predetermined limited movement of the door in a direction against the spring bias; a sensor mounted to the door frame for sensing when the door has been urged by an external force away from its fully closed position to an activation position; a controller for determining when the door has been urged to the activation position for at least a nuisance delay period and providing an alarm signal in response thereto, and thereafter counting an egress time period, and de-energizing the electromagnet at the end of the egress time period; at which point the person who has initiated the process may exit the door.
In another aspect, the armature mounting bolt of the present invention includes: a hollow shaft having a flanged end or head abutting the outside surface of the door, and having an opposite open end; a plunger within the shaft that is capable of moving in a direction coaxial with the shaft, the plunger head being positioned adjacent the shaft flanged end; a spring within the shaft, the spring engaging a lip within the shaft and further engaging the plunger head such that the plunger is biased away from the open shaft end and toward the flanged first end, the lip defining a detent; and a fastener for fastening the armature to the plunger back end. The plunger back end is threaded for engaging the fastener. The shaft is positioned within a hole in the door, and the plunger therefore defines a member that engages the armature and is movable within the volume defined by the door thickness. A threaded cap engages corresponding threads on the back of the shaft, thus retaining the spring and plunger within the shaft. The cap has a hole in it, such that the plunger can move forward and backward while being retained within the shaft.
The above-described objects of the present invention and other features and benefits of the present invention will become clear to those skilled in the art when read in conjunction with the following detailed description of a preferred illustrative embodiment and viewed in conjunction with the attached drawings and appended claims.